In manufacturing a semiconductor device, a substrate cleaning apparatus is used for cleaning a polished wafer. The substrate cleaning apparatus cleans the wafer by engaging a cylindrical roll cleaning tool such as, for example, a roll sponge or a roll brush, against a flat surface of the wafer while supplying a cleaning liquid to the wafer. In the wafer cleaning, it is requested that a load applied to the wafer by the roll cleaning tool be correctly controlled. In practice, however, it is difficult to measure the load on the spot while the wafer is being cleaned by the roll cleaning tool. Therefore, when starting up the substrate cleaning apparatus, a load adjustment (also referred to as a “load calibration”) is performed so as to establish a correlation between a set value of the load and the load that is applied to the wafer.
The load adjustment is performed using a load measuring jig. FIG. 9 is a plan view illustrating a conventional load measuring jig, and FIG. 10 is a front view of the load measuring jig illustrated in FIG. 9. The load measuring jig includes a circular base plate 101 having a diameter that is the same as a wafer W, a load cell 105 attached to the base plate 101, and a load indicator 110 connected to the load cell 105 via a cable 106. The load cell 105 is arranged to be concentric to the base plate 101, and the length of the load cell 105 is about ½ of the diameter of the wafer W.
A recess 101a is formed in the central portion of the base plate 101, and the load cell 105 is placed in the recess 101a. Four (4) thin portions 112, which have substantially the same thickness as the wafer W, are formed in the outer periphery of the base plate 101. The top surfaces of the thin portions 112 are flush with the top surface of the load cell 105.
FIG. 11 is a plan view illustrating the load measuring jig set in a substrate cleaning apparatus in the related art. As illustrated in FIG. 11, the load measuring jig is held by a substrate holding mechanism (wafer holder) of the substrate cleaning apparatus, in a similar way as a wafer W is held. The substrate holding mechanism includes four (4) holding rollers 121, 122, 123, 124, and the outer periphery of the load measuring jig (and the wafer W) is held by the four holding rollers 121, 122, 123, 124.
FIG. 12 is a front view illustrating a state in which the load measuring jig set in the substrate cleaning apparatus measures a load in the related art, and FIG. 13 is a side view illustrating the load measuring jig illustrated in FIG. 12. In measuring the load, the roll cleaning tool is not used, and a dummy roll 115 dedicated to the load measurement is used instead. The dummy roll 115 has the same shape, size, and weight as the roll cleaning tool when the roll cleaning tool contains a cleaning liquid. Such a dummy roll 115 is used because, when a load measurement is performed using the roll cleaning tool containing the cleaning liquid, the cleaning liquid may infiltrate into the load cell 105 so that the load cell 105 may break down.
The dummy roll 115 is made of a material that is harder than the roll cleaning tool. For example, in the case where the roll cleaning tool is made of a polyvinyl alcohol (PVA), the dummy roll 115 is made of polyvinyl chloride (PVC). As illustrated in FIG. 13, the dummy roll 115 is attached to a roll shaft 130 of the substrate cleaning apparatus. The roll shaft 130, the dummy roll 115, and a roll rotating mechanism 133 are supported by a spring 132.
An air cylinder 135, which serves as a load generating apparatus, is connected to the roll rotating mechanism 133. The air cylinder 135 moves the dummy roll 115 downward against the repulsive force of the spring 132. When the load measurement of the dummy roll 115 is performed, the dummy roll 115 is pressed against the load cell 105 without being rotated. The load cell 105 measures the load applied from the dummy roll 115, and a load indicator 110 (see, e.g., FIG. 9) indicates the measured value of the load. See, for example, Japanese Patent Laid-Open Publication Nos. 2014-103387 and 2014-038983.